Hi. Our Vokera linea 24 always provides hot water but the heating is only on very occasionally. We have had an engineer who changed parts but as soon as there is any cold weather the problem returns. The heating occasionally comes on. We tried a new engineer who charged £94 and got heating on. A couple of hours later it went off again. His boss came out next day and got it going at a lower temperature reading on the red gauge. Heating worked fine for one night. It was turned off by the timer. This morning same problem again: Hot water only: no heating. Suggestions please, Ric